Preparation of tungsten powders



Patented Oct. 12, 1926.

UNITED stares PAT Fr es WILLIAM BENJAMIN HERO, F BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

PREPARATION OF TUNGSTEN POWDJERS.

Ho Drawing. Application filed March 18, 1924, Serial No. 700,193. Renewed April 2, 1926.

the quantity and chemical compositions of the constituent elements during certain phases of the process.

A more specific object of the invention is to produce tungsten powders possessing predetermined physical characteristics by' reducing an oxide of tungsten having incorporated therewith definite and known quantities of a compound or compounds containing an alkali metal or metals.

Various uses for tungsten powder possessing different predetermined physical characteristics suggest themselves. For example appreciated by workers in the art, that if the tungsten powder is too fine, it militates against the successful fabrication of the powder to filament form. Furthermore, in obtaining tungsten in the coherent condition, it is desirable to press the same into slugs. of powder into this form, it is recognized that the powder, if fairly coarse, but not Heretofore, no practical methods have been devised for producing tungsten powder possessing uniform particle size, although there are many processes which, when practiced, result in the formation of powder which is composed of fine and course particles varying in size from very fine to very course powder. One of the methods which has been resorted to for producing tungsten powder of fairly uniform article size, is that of reducing the oxide y means of hydrogen and by carefully controlling the rate of reduction and the temperature conditions under which the reduction took place, it was possible to secure a powder which was fairly uniform in size. However, in order to obtain a powder of a different degree of fineness, it was necessary in the manufacture of tungsten wire, it is In order to facilitate the pressing too coarse, will give a more compact slug.

predetermined quantity of a compound or compounds of an alkali metal or metals, thus providing a simple method in which but one factor is required to be varied.

In practicing my invention, I may utilize a tungstic oxide which contains the required amount of the compound containing the alkali metal or metals or I may take a substantially pure tungstic oxide or at least one which is free from any appreciable quantity of an alkali metal compound and add thereto, the desired amounts of the compound of the alkali metal or metals. I have further found that the physical characteristics of the powders resulting from practicing my process vary inversely with the atomic Weight of the alkali metal employed.

More specifically, the discovery which I have made, contemplates for the production of a coarse powder, the reduction of a tungstic oxide which already contains a desired quantity of a compound containing lithium or the addition to a purified tung stic oxide, i. e., one that is substantially free from lithium or any other alkali compound,

a predetermined quantity of a compound containing lithium. The percentage of the compound of lithium which may be added or which may be present in the tungstic oxide at the time of reduction is preferably .5% although this quantity may be varied between about .1% and about 5% as it is. found that it is possible to vary the physical characteristics of the powder by varying the percentage of the alkali metal content. This oxide containing the predetermined or required quantity of a compound containing lithium may then be reduced by means of hydrogen or any other satisfactory reducing agent in a furnace through which the hydrogen or. similar reducing agent is con tinuously passed. Specifically this operation comprises placing, say 200 grams of oxide in an iron boat 3 feet long and passing .the same through a 1 tube, at the rate of 3 feet per hour. Thetube is heated in a furnace which is approximately six feet long. Hydrogen gas is forced through the tube at the rate of 32 cubic feet per hour in the reverse direction in which the boat containing the tungstic oxide travels. Several boats containing the materials may follow directly behind each other so there is an uninterrupted chain. The temperature of the furnace is held varying from about 500 C. at one end to about 700 C. at the other.

It is to be appreciated that variations may be made in the movement of the mixture through the furnace, the temperature employed and the rate of flow of the reducing gas. However, one of the outstanding features of my invention consists in obtaimng the desired particle size of the tungsten by maintaining the furnace conditions substantially constant and merely varying the nature of the doping material in order to ob tain the desired or predetermined physical characteristics in the powder.

I have found that more than 5% of material may be used if desired and also that a correspondingly coarser material is obtained with increased quantities of the doping material. Economic considerations, however, operate in setting a practical limit at that point. If coarser material is desired the same can be obtained either by using high percentages of, say, lithium compounds and low furnace temperatures or by using a moderate quantity and a high temperature; the relative cost of heat and the doping constituents will determine which will be most economical. This reference to the use of higher temperature must not be construed as contradictory to previous statements concerning my process. On the contrary it can be shown that the same differential in particle size would be obtained between different doping materials provided the temperature conditions are sufiicientto effect a reduction of the tungsten. Experiments clearly show that the employment of any of the compounds of the alkali metals gives a coarser tungsten powder than when none are present for the same temperature. It therefore is obvious that my process provides a more economical method of producing coarse tungsten powder than the method formally used which depended principally upon the use of high temperature.

If it is desired to obtain a medium grade powder, the doping material may comprise a COIHPOIlIld containing sodium and if a still finer powder is desired a compound containing potassium may be employed, while still finer powders may be secured by the addition of rubidium and caesium compounds respectively. Inasmuch as the atomic weight of lithium is 7 while that of sodium, potassium, rubidium and caesium is 23, 39, 85

meats? and 133 respectively, it will be noted the lower the atomic weight, the coarser the metal powder that is obtained. In other words, the particle size is inversely proportional to the atomic weight.

Heretofore I have pointed out that the powders prepared in accordance with my process possessed widely variant physical characteristics and it is my belief founded upon the evidence resulting from the test hereinafter disclosed that this variation in physical properties is primarily the result of a variation in the particle or grain size.

Various specimens were obtained by doping tungsten oxide with different alkali metal compounds, and these were reduced under constant temperature and otherwise comparable conditions and each specimen thus obtained was subjected to the following test.

A specimen was weighed and placed in a bottle three inches in height and '7 inch in diameter. Distilled water was run into the bottle to a depth of two inches The powder was then placed in the distilled water and after the bottle was stopped it was vigorously shaken for approximately a half minute. The bottle was then placed in a well lighted place with white paper used as a background against which the dark particles were easily visible. The time in minutes that is required for the powder to settle was taken as the settling time an the termination of the settling period or the end point was reached when the metal in suspension in the water ceased to color the white paper placed in back of the bottle.

The results obtained are tabulated hereunder in accordance with the atomic weight of the alkali metal constituent of the doping material.

' Atomic Doping material (compounds containing) igg g weight of metal Lithium 2 7 Sodium 13 Z3 Potassium I6 39 (minm 25 133 Undnrwd 35 It will be noted from these tests that the time of settling when compared with the atomic weights of the metals of the compounds employed is inverse with respect thereto. In other words, the lower the atomic weight of the alkali metal of the compound employed, the coarser the grade of tungsten power obtained. I have found that it is immaterial which compounds of the alkali metals are employed as equally satisfactory results have been obtained by using either the nitrates or chlorides. The influence which is exerted by the alkali metals is believed to take place at the time that the tungstic oxide' containing the doping material isreduced, as it is during such period that the characteristic efiect on the resulting tungsten powder is observed.

It is also to be appreciated that by practicing' my process,'mixtures of any desired proportions of tungsten powders -possessing fabricated into filament form.

The term predetermined physical characteristics as used in the specification and claims has reference to the particle size of the powder, its apparent density. and color and also its inherent property of influencing or controlling grain growth-when the powder is sintered and formed into a wire or filament.

Various changes in the process outlined above, may occur to those skilled in the art but such as come within the scope of the' appended claims are contemplated by me as falling within my invention.

What is claimed is 1. The method of preparing tungsten powder possessing predetermined physical characteristics which comprises mixing with tungsten oxide, a predeterminedquantity of a compound containing an alkali metal and then reducing the oxide by means of hydrogen.

2; The method of preparing tungsten powder possessing predetermined physical characteristics which comprises mixing with tungsten oxide substantially free from alkali metal contaminations, a. predetermined quantity of a compound containing an alkali metal and then reducing the oxide by means of hydrogen.

3. The method of predetermining particle size of tungsten which comprises mixing with purified tungsten oxide, a predetermined quantity of a compound containing an alkali metal and then reducing-the oxide by means of hydrogen.

4. The method of obtaining tungsten powder possessing predetermined physical characteristics which comprises reducing tungstic oxide in the presence of a predetermined quantity of an alkali metal and simultaneously applying heat.

5. The method of obtaining tungsten powder varying from coarse to fine particle size which comprises mixing with tungstic oxide compounds containing lithium, sodium, potassium, rubidium and caesium, respectively,

and reducing the same by means of hydrogen at an elevated temperature.

' 6. The method of obtaining coarse grained tungsten powder which comprises mixing with purified tungsten oxide between about .1% and about 1% by weight of a compound containing lithium or sodium and reducing the tungsten oxide by means of hydrogen at an elevated temperature.

7. The method of obtaining tungsten of medium grain or particle size which comprises mixing purified tungsten oxide with between about .1% to about 1% of a compound containing either potassium or rubidium, and reducing the oxide by means of hydrogen at an elevated temperature.

8. The method of obtaining tungsten powder of fine grain or particle size which comprises mixing with purified tungsten oxide between about .1% and about 1% of a compound containing caesium and reducing the oxide by means of hydrogen at an elevated temperature.

9. The method of obtaining tungsten of varying grades of coarseness which comprises mixing with tungsten oxide varying percentages of a compound containing lithium and reducing the oxide by means of hydrogen at an elevated temperature.

10. The method of obtaining tungsten of varying grain or particle size which comprises mixing tungsten oxide with a compound containing an alkali metal, the atomic weight of which latter is inversely proportional to the desired grain size, and reducing the oxide by means of hydrogen at an elevated temperature. p

11. The method of controlling the grain size of tungsten which comprises doping tungsten oxide with predetermined quantities of a particular alkali metal and reducing the oxide by means of hydrogen at an elevated temperature.

12. The method of obtaining coarse tungsten powder which comprises doping tungstic oxide with lithium nitrate and reducing the oxide by means of hydrogen at an elevated temperature.

13. The method of obtaining fine tungsten powder which comprises doping tungstic oxide with a predetermined quantity of caesium nitrate and reducing the oxide by means of hydrogen at an elevated temperature.

14:. The method of preparing a mixture of tungsten powders possessing varying predetermined physical characteristics which comprises mixing tungsten oxide with a plurality of compounds containing difierent alkali metals selected in accordance with the physical characteristics desired.

15. Tungsten powder possessing predetermined physical characteristics derived by doping an oxide of tungsten with a selected alkali metal containing compound.

16. Tungsten powder comprising a mixture of powders possessing predetermined physical characteristics derived by doping' tungsten oxide with a plurality of alkali 5 metal containing compounds selected in accordance with the characteristics desired.

17.. Tungsten powder comprising a plurality of particles possessing predetermined physical characteristics resulting from treatin; tungsten oxide with selected alkali metal compounds.

In testimony whereof, I have hereunto subscribed my name this 15th day of March 1924.

WILLIAM BENJAMIN GERO. 

